Process for producing acrylonitrile or methacrylonitrile from propane or isobutane by ammoxidation

ABSTRACT

Process for producing acrylonitrile or methacrylonitrile from propane or isobutane by ammoxidation at a temperature in the range of from 380 to 500° C. in a fluidized-bed reactor containing a catalyst composition preheated to a temperature of not lower than 300° C. and lower than the ammoxidation reaction temperature, the catalyst composition comprising a carrier having supported thereon an oxide catalyst comprising a compound oxide of molybdenum, vanadium, niobium and at least one element selected from tellurium and antimony, wherein the ammoxidation of propane or isobutane is preceded by a specific temperature elevation operation in which the catalyst temperature in the reactor is elevated, while supplying into the fluidized-bed reactor a molecular oxygen-containing gas together with a combustible gas capable of combustion by reaction with the molecular oxygen in the presence of said catalyst composition, until the temperature of the catalyst composition reaches said ammoxidation reaction temperature. The process of the present invention is advantageous in that the temperature elevation of the catalyst can be performed without suffering a deterioration of the catalytic activity during the temperature elevation, thereby allowing the catalyst to fully exhibit its performance.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for producing acrylonitrileor methacrylonitrile from propane or isobutane by ammoxidation. Moreparticularly, the present invention is concerned with a process forproducing acrylonitrile or methacrylonitrile from propane or isobutaneby ammoxidation at a temperature in the range of from 380 to 500° C.(ammoxidation reaction temperature) in a fluidized-bed reactorcontaining a catalyst composition preheated to a temperature of notlower than 300° C. and lower than the ammoxidation reaction temperature,the catalyst composition comprising a carrier having supported thereonan oxide catalyst comprising a compound oxide of molybdenum, vanadium,niobium and at least one element selected from the group consisting oftellurium and antimony, wherein the ammoxidation of propane or isobutaneat the ammoxidation reaction temperature is preceded by a specifictemperature elevation operation in which the temperature of thepreheated catalyst composition in the fluidized-bed reactor is elevated,while supplying into the fluidized-bed reactor a molecularoxygen-containing gas together with a combustible gas capable ofcombustion by reaction with the molecular oxygen in the presence of thecatalyst composition, until the temperature of the catalyst compositionreaches the ammoxidation reaction temperature. By virtue of theabove-mentioned specific temperature elevation operation using both amolecular oxygen-containing gas and a combustible gas when thetemperature of the catalyst composition is 300° C. or higher, theprocess of the present invention is advantageous in that the temperatureelevation of a catalyst comprising a compound oxide of molybdenum,vanadium, niobium and at least one element selected from tellurium andantimony can be performed without suffering a deterioration of thecatalytic activity during the temperature elevation of the catalyst,thereby allowing the catalyst to fully exhibit its inherent performance.

2. Prior Art

It has been well known to produce an unsaturated nitrile, such asacrylonitrile or methacrylonitrile, by ammoxidation of an olefin, suchas propylene or isobutene, namely, by reacting an olefin with ammoniaand molecular oxygen.

On the other hand, from the viewpoint of reducing the cost for rawmaterials, attention has been attracted to a process for producing anunsaturated nitrile (such as acrylonitrile or methacrylonitrile) from analkane (such as propane and isobutane), which is available at low costas compared to an alkene, by ammoxidation in the presence of a catalyst,i.e., by reacting an alkane with ammonia and molecular oxygen in thepresence of a catalyst. Further, a number of proposals have also beenmade with respect to catalysts for use in the ammoxidation of an alkane.

For example, as a catalyst for use in producing acrylonitrile byammoxidation of propane, there is known an oxide catalyst containingmolybdenum, vanadium, tellurium and niobium. Such a catalyst and amethod for producing the catalyst are disclosed in each of JapanesePatent Publication No. 2608768 (published in 1997)(corresponding to U.S.Pat. No. 5,049,692), Unexamined Japanese Patent Application Laid-OpenSpecification No. 5-208136 (corresponding to U.S. Pat. No. 5,281,745)and Unexamined Japanese Patent Application Laid-Open Specification No.6-285372 (corresponding to U.S. Pat. No. 5,422,328). Further, UnexaminedJapanese Patent Application Laid-Open Specification No. 9-157241(corresponding to European Patent No. 767,164) discloses an oxidecatalyst containing molybdenum, vanadium, antimony and niobium as acatalyst for use in producing acrylonitrile by ammoxidation of propane.These prior art documents have a description concerning ammoxidationreaction conditions employed in the evaluation of the performance ofsuch catalyst. However, with respect to the manner of elevating thetemperature of the catalyst before starting the ammoxidation reaction ofpropane, no description is found in these prior art documents.

Unexamined Japanese Patent Application Laid-Open Specification No.10-57813 discloses a process for producing acrylic acid by oxidation ofpropane, using a catalyst containing molybdenum, vanadium and at leastone element selected from tellurium and antimony. In this process, thecatalyst is subjected to heat treatment virtually in the absence ofmolecular oxygen, and then subjected to further heat treatment under astream of air. However, in this prior art document, there is nodescription as to whether or not such a manner of heat treatment in thatprocess is effective for the ammoxidation reaction of propane orisobutane.

Unexamined Japanese Patent Application Laid-Open Specification No.8-225506 (corresponding to U.S. Pat. No. 5,534,650) discloses a methodfor performing an ammoxidation reaction of an alkane in which gaseousammonia is fed into a reactor from a plurality of ammonia inletsprovided therein. However, with respect to the manner of elevating thetemperature of a catalyst before starting the ammoxidation reaction ofan alkane, no description is found in this prior art document.

Japanese Patent Publication No. 2599677 (published in1997)(corresponding to U.S. Pat. No. 5,332,855) discloses anammoxidation method for a saturated hydrocarbon, using a catalyst whichcontains vanadium, antimony and at least one element selected from iron,gallium and indium; Examined Japanese Patent Application Publication No.6-92355 (corresponding to U.S. Pat. No. 5,334,743) discloses anammoxidation method for a saturated hydrocarbon, using a catalyst whichcontains molybdenum, vanadium and at least one element selected frommanganese, zinc, cobalt, copper, lithium, sodium, potassium and silver;and Japanese Patent Publication No. 2506602 (published in1996)(corresponding to U.S. Pat. No. 5,336,804) discloses anammoxidation method for a saturated hydrocarbon, using a catalyst whichcontains vanadium, antimony and bismuth. In these prior art documents,there is a description about an evaluation method for the ammoxidationreaction, in which the temperature of a catalyst contained in a reactoris first elevated to 150° C. while purging the air in the reactor withhelium, and then feedstock gases and diluent gases, i.e., propane,ammonia, oxygen, steam and helium, are fed while further elevating thetemperature of the catalyst to a predetermined temperature, for example,300° C., whereupon the catalyst temperature is maintained at thepredetermined temperature for 30 minutes, followed by analysis of agaseous mixture withdrawn from the outlet of the reactor. The presentinventors conducted experiments in which the catalysts described inthese prior art documents were produced and ammoxidation reactions wereconducted using the produced catalysts individually to make variousevaluations. As a result, it was found that the performance of thecatalyst is almost not affected by the type of gas which is suppliedinto a reactor containing the catalyst during the elevation of thetemperature of the catalyst before starting the ammoxidation reaction.More specifically, the catalyst exhibits the same performanceirrespective of whether the gas used during the temperature elevation isair alone or air plus combustible gas selected from feedstock gases.

As a method for the ammoxidation of an olefin by using a catalyst whichcontains antimony and uranium, British Patent No. 1,304,665 discloses amethod in which a catalyst bed comprising a regeneration zone and areaction zone located adjacent to each other is provided, and molecularoxygen necessary for the ammoxidation is flowed through the regenerationzone of the catalyst bed, together with ammonia in an amount of 3% ormore of the whole amount of ammonia to be fed. In this method, thefeeding of ammonia to the regeneration zone is intended to suppress aloss of propylene in the regeneration zone. In this prior art document,there is no description as to the manner of elevating the temperature ofthe catalyst bed before the start of the ammoxidation reaction ofpropylene.

U.S. Pat. No. 4,814,478 discloses a method in which the ammoxidationreaction of a saturated hydrocarbon is performed using a mixed catalystof a catalyst comprised mainly of vanadium and antimony and a catalystcomprised mainly of molybdenum, bismuth and iron. In this prior artdocument, as a specific example of the reaction method, a method using afixed-bed reactor is described, wherein gaseous raw materials arepreheated by means of a "preheat leg", and the resultant preheatedgaseous raw materials are then introduced into a catalyst bed. However,this prior art document has no description as to the manner of elevatingthe temperature of the catalyst bed before starting the ammoxidationreaction.

U.S. Pat. No. 3,833,638 discloses a catalyst for use in the ammoxidationreaction of a saturated hydrocarbon. The catalyst contains molybdenum,cerium and at least one element selected from the group consisting ofbismuth and tellurium. In this prior art document, it is described thatgaseous raw materials can be fed to the reactor either before or afterthe internal temperature of the reactor reaches a desired reactiontemperature. In this connection, it is noted that the catalyst of thisprior art document is of a type such that the regeneration of thecatalyst can be performed through contact with air at high temperatures.Therefore, with respect to the technique of this prior art document, itis preferred that the elevation of the internal temperature of thereactor toward a desired reaction temperature is performed whilesupplying air into the reactor, and the feeding of gaseous raw materialsis started after the internal temperature of the reactor has reached thedesired reaction temperature.

As described hereinabove, various proposals have been made to provide animproved process for producing an unsaturated nitrile by ammoxidation ofan alkane (such as propane and isobutane) in the presence of a catalyst.However, such proposals have been disadvantageous in that the catalyticactivity of the specific catalyst (comprising a carrier having supportedthereon an oxide catalyst comprised of a compound oxide of molybdenum,vanadium, niobium and at least one element selected from the groupconsisting of tellurium and antimony) cannot be maintained at a highlevel when the ammoxidation reaction is performed. Therefore, it hasbeen desired to develop an improved process for producing an unsaturatednitrile from an alkane by ammoxidation, which can maintain the catalyticactivity of the catalyst at a high level even after the temperature ofthe catalyst is elevated to the ammoxidation reaction temperature.

SUMMARY OF THE INVENTION

In this situation, the present inventors have conducted extensive andintensive studies with a view toward developing an improved process forproducing an unsaturated nitrile from an alkane by ammoxidation, whichcan provide a satisfactorily high catalytic activity. As a result, ithas unexpectedly been found that, in a process for producingacrylonitrile or methacrylonitrile from propane or isobutane byammoxidation at a temperature in the range of from 380 to 500° C.(ammoxidation reaction temperature) in a fluidized-bed reactorcontaining a catalyst composition preheated to a temperature of notlower than 300° C. and lower than the ammoxidation reaction temperature,the catalyst composition comprising a carrier having supported thereonan oxide catalyst comprising a compound oxide of molybdenum, vanadium,niobium and at least one element selected from the group consisting oftellurium and antimony, it is very effective for attaining the aboveobjective to precede the ammoxidation of propane or isobutane at theammoxidation reaction temperature by a specific temperature elevationoperation in which the temperature of the catalyst composition in thefluidized-bed reactor is elevated, while supplying into thefluidized-bed reactor a molecular oxygen-containing gas together with acombustible gas capable of combustion by reaction with the molecularoxygen in the presence of the catalyst composition, until thetemperature of the catalyst composition reaches the ammoxidationreaction temperature. The present invention has been completed, based onthe above novel finding.

It is, therefore, a primary object of the present invention to providean improved process for producing acrylonitrile or methacrylonitrilefrom propane or isobutane by ammoxidation in a fluidized-bed reactorcontaining a catalyst composition comprising a carrier having supportedthereon a catalyst comprised of a compound oxide of molybdenum, vanadiumand niobium as well as tellurium and/or antimony, in which thetemperature of the catalyst composition can be elevated toward apredetermined ammoxidation reaction temperature using anoxygen-containing gas, such as air, without suffering a deterioration ofthe catalytic activity of the catalyst.

The foregoing and other objects, features and advantages of the presentinvention will be apparent from the following detailed description takenin connection with the accompanying drawing and the appended claims.

BRIEF DESCRIPTION OF DRAWING

In the drawing:

FIG. 1 is a diagrammatic view showing an example of a fluidized-bedreactor suitably employable when the process of the present invention ispracticed for commercial-scale production of acrylonitrile ormethacrylonitrile.

DESCRIPTION OF REFERENCE NUMERALS

1: Line for introducing air

2: Line for introducing ammonia and/or propane

3: Fluidized catalyst bed

4: Outlet for the produced gas

5: Line for the effluent

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, there is provided a process for producingacrylonitrile or methacrylonitrile from propane or isobutane byammoxidation at a temperature in the range of from 380 to 500° C.(ammoxidation reaction temperature) in a fluidized-bed reactorcontaining a catalyst composition comprising a carrier having supportedthereon an oxide catalyst, the oxide catalyst comprising a compoundoxide of molybdenum, vanadium, niobium and at least one element selectedfrom the group consisting of tellurium and antimony,

the process comprising:

(1) providing a fluidized-bed reactor containing the catalystcomposition preheated to a temperature of not lower than 300° C. andlower than the ammoxidation reaction temperature;

(2) elevating the temperature of the preheated catalyst composition inthe fluidized-bed reactor, while supplying into the fluidized-bedreactor a molecular oxygen-containing gas together with a combustiblegas capable of combustion by reaction with the molecular oxygen in thepresence of the catalyst composition, until the temperature of thecatalyst composition reaches the ammoxidation reaction temperature; and

(3) changing the supply of the combustible gas and the molecularoxygen-containing gas into the fluidized-bed reactor to a feeding ofpropane or isobutane, ammonia and molecular oxygen into thefluidized-bed reactor when the temperature of the catalyst compositionreaches the ammoxidation reaction temperature, to thereby effect anammoxidation reaction of the propane or isobutane, thus producingacrylonitrile or methacrylonitrile.

For an easy understanding of the present invention, the essentialfeatures and various preferred embodiments of the present invention areenumerated below.

1. A process for producing acrylonitrile or methacrylonitrile frompropane or isobutane by ammoxidation at a temperature in the range offrom 350 to 550° C. (ammoxidation reaction temperature) in afluidized-bed reactor containing a catalyst composition comprising acarrier having supported thereon an oxide catalyst, the oxide catalystcomprising a compound oxide of molybdenum, vanadium, niobium and atleast one element selected from the group consisting of tellurium andantimony,

the process comprising:

(1) providing a fluidized-bed reactor containing the catalystcomposition preheated to a temperature of not lower than 300° C. andlower than the ammoxidation reaction temperature;

(2) elevating the temperature of the preheated catalyst composition inthe fluidized-bed reactor, while supplying into the fluidized-bedreactor a molecular oxygen-containing gas together with a combustiblegas capable of combustion by reaction with the molecular oxygen in thepresence of the catalyst composition, until the temperature of thecatalyst composition reaches the ammoxidation reaction temperature; and

(3) changing the supply of the combustible gas and the molecularoxygen-containing gas into the fluidized-bed reactor to a feeding ofpropane or isobutane, ammonia and molecular oxygen into thefluidized-bed reactor when the temperature of the catalyst compositionreaches the ammoxidation reaction temperature, to thereby effect anammoxidation reaction of the propane or isobutane, thus producingacrylonitrile or methacrylonitrile.

2. The process according to item 1 above, wherein the combustible gas isat least one compound selected from the group consisting of C₁ -C₈alkanes, C₂ -C₈ alkenes, C₂ -C₄ alkynes, C₄ -C₅ dienes, C₃ -C₈cycloalkanes, C₄ -C₈ cycloalkenes, C₆ -C₉ aromatic hydrocarbons, C₁ -C₈alcohols, C₂ -C₇ ethers, C₁ -C₃ aldehydes, C₂ -C₃ epoxides, C₂ -C₈ketones, C₁ -C₄ nitriles, C₁ -C₄ carboxylic acids, C₂ -C₅ esters, C₁ -C₆nitrogen-containing organic compounds, C₁ -C₄ sulfur-containing organiccompounds, hydrogen, ammonia, carbon monoxide, hydrogen sulfide andcarbon disulfide.

3. The process according to item 1 above, wherein the combustible gas isat least one compound selected from the group consisting of propane,isobutane, propylene, isobutene, methanol, ethanol, propanol, hydrogen,ammonia and carbon monoxide.

4. The process according to item 1 above, wherein the combustible gas isammonia.

5. The process according to any one of items 1 to 4 above, wherein thecatalyst composition is obtained by a method comprising:

providing a catalyst composition precursor comprising silica andcompounds of molybdenum, vanadium, niobium and at least one elementselected from the group consisting of tellurium and antimony, and

calcining the catalyst composition precursor in an atmosphere of inertgas which is substantially free of molecular oxygen, to thereby obtain acatalyst composition comprising a silica carrier having supportedthereon an oxide catalyst, the carrier being present in an amount offrom 10 to 70% by weight, based on the total weight of the silica andthe oxide catalyst, the oxide catalyst comprising a compound oxide beingrepresented by the following formula (1):

    Mo.sub.1.0 i V.sub.a Nb.sub.b A.sub.c O.sub.x              (1)

wherein:

A is at least one element selected from the group consisting oftellurium and antimony;

and

a, b, c and x are, respectively, the atomic ratios of vanadium, niobium,A and oxygen, relative to the molybdenum,

wherein

a is a number from 0.01 to 1.0;

b is a number from 0.01 to 1.0;

c is a number from 0.01 to 1.0;

and

x is a number determined by the valence requirements of the otherelements present.

Hereinbelow, the present invention will be described in more detail.

During the temperature elevation of a catalyst composition contained ina fluidized-bed reactor until the temperature reaches an ammoxidationreaction temperature, for uniformly heating the catalyst composition, itis necessary to keep the catalyst composition in a fluidized state bysupplying gas, such as air, into the fluidized-bed reactor. The catalystcomposition used in the process of the present invention contains anoxide catalyst comprising a compound oxide of molybdenum, vanadium,niobium and at least one element selected from the group consisting oftellurium and antimony. It has been found that, when the catalystcomposition used in the process of the present invention is contactedwith a molecular oxygen-containing gas, such as air, during the courseof the temperature elevation of the catalyst composition to theammoxidation reaction temperature, a change occurs in the catalyststructure as determined by an X-ray diffraction measurement, causing adeterioration of the catalytic activity of the catalyst, so thatproblems arise, such as a lowering of the conversion of propane andisobutane and a lowering of the yield of acrylonitrile ormethacrylonitrile.

However, the present inventors have unexpectedly found that thedeterioration of the catalyst composition, which is likely to occur bycontact of the catalyst composition with a molecular oxygen-containinggas during the temperature elevation of the catalyst composition, can beprevented by (1) providing a fluidizedbed reactor containing thecatalyst composition preheated to a temperature of not lower than 300°C. and lower than the ammoxidation reaction temperature, and (2)performing a specific temperature elevation operation in which thetemperature of the preheated catalyst composition in the fluidized-bedreactor is elevated, while supplying into the fluidized-bed reactor amolecular oxygen-containing gas together with a combustible gas capableof combustion by reaction with the molecular oxygen in the presence ofthe catalyst composition, until the temperature of the catalystcomposition reaches the ammoxidation reaction temperature.

Combustible gases used in the present invention mean gases which cancombust when it is reacted with molecular oxygen at 300° C. or higher inthe presence of the catalyst composition used in the process of thepresent invention.

Examples of combustible gases used in the process of the presentinvention include organic compounds, such as C₁ -C₈ alkanes (e.g.,methane, ethane, propane, n-butane, isobutane, pentane, hexane, heptaneand octane), C₂ -C₈ alkenes (e.g., ethylene, propylene, n-butene,isobutene, pentene, hexene, heptene and octene), C₂ -C₄ alkynes (e.g.,acetylene, methylacetylene and dimethylacetylene), C₄ -C₅ dienes (e.g.,butadiene and isoprene), C₃ -C₈ cycloalkanes (e.g., cyclopropane,cyclobutane, cyclopentane, cyclohexane, cycloheptane and cyclooctane),C₃ -C₈ cycloalkenes (e.g., cyclopropene, cyclobutene, cyclopentene,cyclohexene, cycloheptene and cyclooctene), C₆ -C₉ aromatic hydrocarbons(e.g., benzene, toluene, xylene, ethylbenzene, propylbenzene andstyrene), C₁ -C₈ alcohols (e.g., methanol, ethanol, propanol, butanol,pentanol, hexanol, heptanol and octanol), C₂ -C₇ ethers (e.g., dimethylether, diethyl ether, anisol, tetrahydrofuran, furan and dioxane), C₁-C₄ aldehydes (e.g., formaldehyde, acetaldehyde, propionaldehyde andvaleraldehyde), C₂ -C₃ epoxides (e.g., ethylene oxide and propyleneoxide), C₂ -C₈ ketones (e.g., acetone, methyl ethyl ketone, diethylketone and methyl benzyl ketone), C₁ -C₄ nitriles (e.g., hydrogencyanide, acetonitrile, propionitrile, acrylonitrile, methacrylonitrileand isobutyronitrile), C₁ -C₄ carboxylic acids (e.g., formic acid,acetic acid, propionic acid and valeric acid), C₂ -C₆ esters (e.g.,methyl formate, ethyl formate, methyl acetate, ethyl acetate, methylpropionate, ethyl propionate, methyl valerate and ethyl valerate), C₁-C₆ nitrogen-containing organic compounds (e.g., methylamine,dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine,aniline, pyridine, nitromethane and nitroethane), C₁ -C₄sulfur-containing organic compounds (e.g., methyl mercaptan, thiophene,dimethyl thioether and diethyl thioether); and inorganic compounds, suchas hydrogen, ammonia, carbon monoxide, hydrogen sulfide, and carbondisulfide. Of these compounds, preferred are propane, isobutane,propylene, isobutene, methanol, ethanol, propanol, hydrogen, ammonia andcarbon monoxide. More preferred are propane, isobutane, propylene,isobutene and ammonia. Especially preferred is ammonia. These compoundscan be used individually or in combination.

In the process of the present invention, with respect to the amount ofthe combustible gas supplied into the fluidized-bed reactor during thecourse of the temperature elevation when the temperature of the catalystcomposition (hereinafter, frequently referred to simply as "catalysttemperature") is 300° C. or higher, there is no particular limitation aslong as the effects of the present invention can be achieved and thecomposition of a gaseous mixture effluent from an outlet of the reactoris maintained outside of an explosion range as measured at the outlet.However, the lower limit of the amount of the combustible gas isgenerally in the range of 0.1% by volume or more, preferably 0.5% byvolume or more, more preferably 1.0% by volume or more, based on thetotal volume of the molecular oxygen-containing gas and the combustiblegas both supplied into the reactor during the course of the temperatureelevation when the catalyst temperature is 300° C. or higher. Withrespect to the selection of the upper limit of the amount of thecombustible gas, it is desirable to take into consideration aneconomical disadvantage caused by the use of too large an amount of thecombustible gas. Therefore, the upper limit of the amount of thecombustible gas is generally in the range of 30% by volume or less,preferably 25% by volume or less, more preferably 20% by volume or less,based on the total volume of the molecular oxygen-containing gas and thecombustible gas both supplied into the reactor during the course of thetemperature elevation when the catalyst temperature is 300° C. orhigher.

Elucidation has not yet been made with respect to the reason why, in theprocess of the present invention, a deterioration of the catalyticactivity of the catalyst, which occurs by contact of the catalyst with amolecular oxygen-containing gas supplied during the temperatureelevation, can be prevented by supplying a combustible gas, togetherwith the molecular oxygen-containing gas, into the reactor during thecourse of the temperature elevation when the catalyst temperature is300° C. or higher. However, it is considered that during the course ofthe temperature elevation when the catalyst temperature is 300° C. orhigher, the combustible gas is adsorbed on the surface of the catalystand the adsorbed combustible gas reacts with the molecular oxygen of themolecular oxygen-containing gas, thereby preventing the catalyst fromundergoing oxidative deterioration before the start of the ammoxidationreaction. Further, with respect to the reason why such unexpectedexcellent effects of the present invention for preventing thedeterioration of the catalytic activity can be exhibited even when onlya small amount of the combustible gas is supplied into the reactor, thereason is believed to be as follows. In a fluidized-bed reactor, thecatalyst particles are freely moved in the vertical and horizontaldirections. Therefore, even if the amount of the combustible gassupplied into the reactor is small, the combustible gas is smoothly,uniformly dispersed in the fluidized catalyst bed, so that the entire ofthe catalyst is effectively contacted with the combustible gas.

In the process of the present invention, the supply of a combustible gasmay be started at the catalyst temperature of 300° C. or higher,preferably between 300 and 380° C.

Examples of manners of supplying a combustible gas into the reactor inthe process of the present invention include a method in which thecombustible gas is supplied into the reactor in the form of a mixturethereof with the molecular oxygen-containing gas, and a method in whichthe combustible gas and the molecular oxygen-containing gas areseparately supplied into the reactor through separate supply linestherefor.

The term "oxygen-containing gas" used herein means a mixture ofmolecular oxygen and a gas which is inert to the combustion reaction ofa combustible gas.

Examples of molecular oxygen-containing gases supplied into the reactorduring the course of the temperature elevation include air; a gaseousmixture obtained by diluting air with inert gas, such as nitrogen,argon, steam and carbon dioxide, so as to lower the oxygen concentrationof the air; a gaseous mixture obtained by adding oxygen to air so as toincrease the oxygen concentration of the air; a gas obtained byincreasing the nitrogen or oxygen concentration of air by membraneseparation or pressure swing adsorption (PSA); and pure oxygen gas.Among these molecular oxygen-containing gases, from an economical pointof view, air can be most advantageously used.

In the process of the present invention, the ammoxidation reactiontemperature is generally in the range of from 380 to 500° C., preferablyfrom 400 to 470° C. The ammoxidation reaction pressure may generally bein the range of from atmospheric pressure to 3 atm. The time of contact(contact time) between gaseous feedstocks (i.e., propane or isobutane,ammonia and molecular oxygen) and the catalyst composition may generallybe from 0.1 to 20 (sec·g/cc), preferably from 0.5 to 10 (sec·g/cc). Inthe process of the present invention, the contact time during theammoxidation reaction of propane or isobutane is determined according tothe following formula: ##EQU1## wherein: W represents the weight (g) ofthe catalyst composition contained in the fluidized-bed reactor;

F represents the flow rate (cc/sec) of the gaseous feedstocks [in termsof the value under the normal temperature and pressure conditions (0°C., 1 atm)];

T represents the ammoxidation reaction temperature (°C.); and

P represents the ammoxidation reaction pressure (kg/cm² ·G).

The linear velocity (LV) of the gaseous feedstocks fed into thefluidized-bed reactor is generally from 0.5 to 200 (cm/sec), preferablyfrom 1 to 100 (cm/sec). In the present invention, the linear velocity(LV) is determined according to the following formula: ##EQU2## wherein:S represents the horizontal inner cross-sectional area (cm²) of acylindrical fluidized-bed reactor; and

F, T and P are as defined above.

In the process of the present invention, when the temperature of thecatalyst composition reaches the ammoxidation reaction temperature, thesupply of the combustible gas and the molecular oxygen-containing gasinto the fluidized-bed reactor is changed to a feeding of propane orisobutane, ammonia and molecular oxygen (gaseous feedstocks) into thefluidized-bed reactor (that is, a transformation of a gas compositionfrom the composition for the temperature elevation to the compositionfor the ammoxidation reaction is effected), to thereby effect anammoxidation reaction of the propane or isobutane, thus producingacrylonitrile or methacrylonitrile. When the combustible gas used in thetemperature elevation is comprised of one member selected from ammonia,propane, isobutane, a combination of ammonia and propane and acombination of ammonia and isobutane, the ammoxidation reaction ofpropane or isobutane can be started by, for example, a method in which,after the catalyst temperature has almost reached a predeterminedammoxidation reaction temperature, the composition of the molecularoxygen-containing gas (further containing a combustible gas), which issupplied into the reactor during the course of the temperature elevationwhen the catalyst temperature is 300° C. or higher, is gradually changed(transformed) to a composition of gaseous feedstocks which is suitablefor the ammoxidation reaction, while also gradually changing theconditions in the reactor to ammoxidation conditions, namely, conditionswhich fall within the above-mentioned ranges with respect to thetemperature, pressure, contact time, linear velocity of gaseousfeedstocks and catalyst amount. On the other hand, when the combustiblegas used in the temperature elevation is other than ammonia, propane,isobutane or a combination of ammonia and propane (or isobutane), theammoxidation reaction of propane or isobutane can be started by, forexample, a method in which, after the catalyst temperature has almostreached a predetermined ammoxidation reaction temperature, the amount ofthe combustible gas supplied into the reactor is gradually decreasedwhile starting the feeding of and gradually increasing the amounts ofammonia and propane or isobutane so that the composition of the gasesentering the reactor is gradually changed (transformed) to a suitablecomposition of gaseous feedstocks for the ammoxidation reaction, andwhile also gradually changing the conditions in the reactor toammoxidation reaction conditions, namely conditions which fall withinthe above-mentioned ranges with respect to the temperature, pressure,contact time, linear velocity of gaseous feedstocks and catalyst amount.

With respect to the manner of the supplying each of the molecularoxygen-containing gas and the combustible gas during the course of thetemperature elevation when the temperature of the catalyst compositionis 300° C. or higher, there is no particular limitation, and each ofthese gases can be supplied either continuously or intermittently. Thatis, the supply of any of these gases may be temporarily stopped.However, it is preferred that both of the molecular oxygen-containinggas and the combustible gas are continuously supplied into the reactor.

With respect to the change-starting temperature (transformationthreshold temperature) at which it is started to make a change from thesupply of the molecular oxygen-containing gas in combination with thecombustible gas into the reactor to a feeding of gaseous feedstocks forthe ammoxidation reaction, there is no particular limitation. However,it is preferred that the above change-starting temperature is theammoxidation reaction temperature, or that the above change-startingtemperature is a temperature in the range of ±50° C., moreadvantageously ±30° C., relative to the ammoxidation reactiontemperature.

The term "ammoxidation reaction of propane or isobutane" used in thepresent invention means a reaction of propane or isobutane with ammoniaand molecular oxygen under substantially constant reaction conditions,so that acrylonitrile or methacrylonitrile is steadily produced.

A specific example of the process of the present invention is explainedhereinbelow, referring to FIG. 1 of the accompanying drawing, whichdiagrammatically shows an example of a fluidized-bed reactor suitablyemployable when the process of the present invention is practiced forcommercial-scale production of acrylonitrile or methacrylonitrile. Inthe example of the process of the present invention described below,ammonia is used as the combustible gas, and ammoxidation of propane isconducted.

First, a catalyst composition is charged into a fluidized-bed reactor.Air is externally heated by means of a heat exchanger utilizing heatgenerated by the combustion of a hydrocarbon fuel, and the resultantheated air is continuously supplied into a lower portion of thefluidized-bed reactor through line 1 for introducing air, in thedirection indicated by the arrow depicted along line 1 in FIG. 1 andthrough a perforated bottom plate at the forward end of line 1, therebyproviding fluidized catalyst bed 3 and also elevating the temperature ofcatalyst bed 3 from room temperature to 300° C. or higher. (The mannerof preheating the catalyst bed to 300° C. or higher is not limited tothe above manner, but various other manners can be mentioned, forexample, preheating of the catalyst composition outside of the reactorand transferring of the preheated catalyst composition into the reactor,preheating of the catalyst composition in an atmosphere of inert gas,and the like.) The air in the reactor is discharged through outlet 4 andline 5 in the direction indicated by the arrow depicted along line 5 inFIG. 1. Then, simultaneously with the supply of air into the reactorthrough line 1, ammonia is continuously supplied into a lower portion ofthe reactor through line 2, in the direction indicated by the arrowdepicted along line 2 in FIG. 1, and through a sparger (which ispositioned at the forward end portion of line 2), and the catalysttemperature is further elevated by the heat of combustion due to thecombustion reaction of the ammonia (NH₃ +3/40₂ →1/2N₂ +3/2H₂ O). Duringthe course of the temperature elevation, the amount of ammonia beingsupplied into the reactor is gradually increased until the amount ofammonia being supplied becomes 10 to 20% by volume, based on the totalvolume of air and ammonia both being supplied into the reactor, and thecatalyst temperature is adjusted to about 430° C. After the catalysttemperature has reached about 430° C., the feeding of propane into thereactor is started while continuing to feed ammonia and air into thereactor for the ammoxidation reaction, and propane is fed through line 2in the direction indicated by the arrow depicted along line 2 in FIG. 1,and the amount of propane fed is gradually increased while adjusting theproportions of propane, ammonia and air to a value within a rangesuitable for the ammoxidation reaction. At the same time, the conditionsin the reactor are gradually changed toward ammoxidation reactionconditions which fall within appropriate predetermined ranges oftemperature, pressure, contact time, linear velocity of gaseousfeedstocks and catalyst amount. In this manner, the ammoxidationreaction of propane can be conducted in a steady state. The producedacrylonitrile flows out of the reactor through outlet 4 and line 5 inthe direction indicated by the arrow depicted along line 5 in FIG. 1.(During the temperature elevation and the ammoxidation reaction, thecomposition of a gaseous mixture effluent from outlet 4 of the reactoris controlled so as to be maintained outside of an explosion range.)

After termination of the ammoxidation reaction, the catalyst temperaturein the fluidized-bed reactor may be lowered. During the lowering of thecatalyst temperature, when the catalyst at 300° C. or higher iscontacted with molecular oxygen, the catalyst is likely to bedeteriorated. However, this deterioration of the catalyst can beprevented by supplying into the reactor a combustible gas (as definedabove) together with a molecular oxygen-containing gas during the courseof the temperature lowering when the catalyst temperature is 300° C. orhigher.

The catalyst composition used in the process of the present inventioncontains an oxide catalyst comprising a compound oxide of molybdenum,vanadium, niobium and at least one element selected from tellurium andantimony.

Specific examples of compound oxides include a compound oxiderepresented by the following formula (1):

    Mo.sub.1.0 V.sub.a Nb.sub.b A.sub.c O.sub.x                (1)

wherein:

A is at least one element selected from the group consisting oftellurium and antimony;

and

a, b, c and x are, respectively, the atomic ratios of vanadium, niobium,A and oxygen, relative to the molybdenum,

wherein

a is a number from 0.01 to 1.0, preferably from 0.1 to 0.5;

b is a number from 0.01 to 1.0, preferably from 0.05 to 0.5;

c is a number from 0.01 to 1.0, preferably from 0.05 to 0.5; and

x is a number determined by the valence requirements of the otherelements present.

The oxide catalyst contained in the catalyst composition used in theprocess of the present invention may further contain, in an atomic ratioof 0.3 or less relative to one atom of the molybdenum, at least oneelement selected from tantalum, tungsten, titanium, zirconium, hafnium,iron, chromium, manganese, rhenium, ruthenium, cobalt, rhodium, nickel,palladium, osmium, iridium, platinum, copper, silver, zinc, cadmium,boron, aluminum, gallium, indium, thallium, germanium, tin, lead,phosphorus, bismuth, selenium, scandium, yttrium, lanthanum, cerium,praseodymium, neodymium, samarium, gadolinium, alkali metals andalkaline earth metals.

The catalyst composition used in the process of the present inventioncomprises a carrier having supported thereon an oxide catalyst. Examplesof carriers used in the present invention include silica, alumina,silica-alumina, magnesia, titania and zirconia. Among these carriers,preferred is silica. These carriers can be used individually or in theform of a composite thereof.

With respect to the catalyst composition used in the present invention,the carrier is preferably present in an amount of from 10 to 70% byweight, more preferably 20 to 60% by weight, based on the total weightof the carrier and the oxide catalyst.

With respect to the form of the source of each component element for thecatalyst used in the process of the present invention, there is noparticular limitation as long as the source contains a desired element.Representative examples of sources of component elements for thecatalyst composition used in the present invention include ammoniumparamolybdate [(NH₄)₆ Mo₇ O₂₄ ·4H₂ O] as a source of molybdenum;ammonium metavanadate (NH₄ VO₃) as a source of vanadium; niobiumhydrogenoxalate [Nb(HC₂ O₄)₅ ·nH₂ O] and niobic acid (Nb₂ O₅ ·nH₂ O) asa source of niobium; telluric acid (H₆ TeO₆) as a source of tellurium;and antimony trioxide (Sb₂ O₃) as a source of antimony.

Further examples of sources of component elements for the catalystinclude oxides, ammonium salts, nitrates, chlorides, sulfates andorganic acid salts of desired elements.

With respect to the source of a component element for the carrier usedin the catalyst composition, there is no particular limitation as longas the source contains a desired element for the carrier. Examples ofsources of component elements for the carrier include oxides,hydroxides, inorganic salts and organic salts of desired elements.Further, a source in the form of a sol or a gel can also be used.

The catalyst composition used in the process of the present inventioncan be produced, for example, as follows.

A slurry of raw materials for the catalyst composition used in thepresent invention can be prepared, for example, as follows: sources ofelements, such as molybdenum, vanadium and tellurium, are dissolved inwater or an aqueous solution of nitric acid, and a source of a componentelement for the carrier is added to the resultant solution, followed byfurther addition of a solution of a source of niobium, to thereby obtaina slurry. Further, with respect to antimony and vanadium, a slurry orsolution containing antimony and vanadium, which is obtained by addingantimony oxide to an aqueous solution of ammonium metavanadate, followedby heat treatment under reflux conditions, can also be suitably used. Inthe preparation of the slurry, the order of mixing together solutions ofraw materials can be arbitrarily changed.

The above-mentioned slurry of raw materials can be dried by subjectingit to spray drying to thereby obtain a dried catalyst compositionprecursor in the form of a spherical particulate powder.

The dried catalyst composition precursor obtained in the above-mentionedmanner is subjected to calcination in an atmosphere of inert gas, suchas gaseous nitrogen, argon and helium, which is substantially free ofmolecular oxygen, at a temperature of 450 to 800° C., preferably 500 to700° C. for 1 to 20 hours, thereby obtaining a catalyst compositioncomprising a carrier having supported thereon an oxide catalystcomprising a compound oxide.

With respect to the inert gas for use in the calcination, which issubstantially free of molecular oxygen, the concentration of molecularoxygen in the inert gas is preferably 800 ppm or less, more preferably500 ppm or less, especially preferably 200 ppm or less.

The dried catalyst composition precursor obtained in the above-mentionedmanner may be heat-treated in an atmosphere of air at a temperature of150 to 450° C. before the calcination.

For the heat-treatment and calcination, use can be made of a kiln, suchas a rotary kiln, a tunnel kiln, a muffle kiln and a fluidized firingkiln, in which the conditions of the internal atmosphere can becontrolled.

Thus, a catalyst composition, which has excellent fluidity and abrasionresistance and therefore can be suitably used for a fluidized bedreaction, can be obtained.

With respect to the gaseous feedstock used for the ammoxidation reactionin the process of the present invention, propane or isobutane can beused, and propane is especially preferred. Ammonia used in the processof the present invention need not be of a very high purity but may be ofa commercial grade.

In the process of the present invention, as a source of molecularoxygen, air is generally preferred from an economical view point. Afurther example of a source of molecular oxygen is a gaseous mixtureobtained by, for example, adding molecular oxygen to air so as toincrease the oxygen concentration of the air. Gaseous feedstocks for theammoxidation reaction may be diluted with inert gas (such as helium,argon, nitrogen or carbon dioxide), steam or the like.

The molar ratio of each of ammonia and molecular oxygen to propane orisobutane used for the ammoxidation reaction can be appropriatelyselected in accordance with the type of the reaction mode used, such asa one-pass mode and a recycling mode. For example, when the ammoxidationreaction is conducted by a one-pass mode, for increasing the conversionof the propane or isobutane, the molar ratio of ammonia to propane orisobutane is generally 0.8 to 4, preferably 1 to 3, and the molar ratioof molecular oxygen to propane or isobutane is generally 0.5 to 6,preferably 1 to 4. Further, when unreacted propane or isobutane in theammoxidation reaction is recycled (i.e., when a recycling mode is used),for increasing the selectivity for a desired unsaturated nitrile namely,acrylonitrile or methacrylonitrile, it is preferred that the reaction isconducted under conditions wherein the conversion of propane orisobutane is suppressed to a level as low as possible. Therefore, when arecycling mode is used, the molar ratio of ammonia to propane orisobutane is generally 0.1 to 1, preferably 0.2 to 0.8, and the molarratio of molecular oxygen to propane or isobutane is generally 0.1 to 4,preferably 0.2 to 2.

With respect to propane or isobutane used in the process of the presentinvention, the propane or isobutane may be mixed into ammonia and amolecular oxygen-containing gas, and then the resultant gaseousfeed-stock mixture can be fed into the reactor. Further, propane orisobutane may first be mixed with ammonia to obtain a gaseous mixture ofpropane or isobutane and ammonia, and then the obtained gaseous mixtureand a molecular oxygen-containing gas can be individually, separatelyfed into the reactor so as to allow them to be mixed and contacted witheach other. Further, propane or isobutane, ammonia and a molecularoxygen-containing gas may be individually, separately fed into thereactor so as to allow them to be mixed and contacted with each other inthe reactor. Still further, each of ammonia and a molecularoxygen-containing gas may be fed into the reactor in a stepwise manner.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the present invention will be described in more detail withreference to the following Examples and Comparative Examples as well asReference Example, which should not be construed as limiting the scopeof the present invention.

In the following Examples and Comparative Examples, the conversion (%)of propane and the yield (%) of acrylonitrile, both used for evaluatingthe results of the ammoxidation reaction of propane, are defined asfollows: ##EQU3##

REFERENCE EXAMPLE

(Preparation of a catalyst composition)

A catalyst composition comprising a silica carrier having supportedthereon an oxide catalyst, wherein the silica carrier is present in anamount of 30% by weight, based on the total weight of the silica carrierand the oxide catalyst, and wherein the oxide catalyst comprises acompound oxide represented by the formula: Mo₁.0 V₀.33 Nb₀.11 Te₀.22O_(x), was prepared as follows.

356.7 g of ammonium metavanadate (NH₄ VO₃) was dissolved in 7,200 g ofwater at a temperature of about 60° C. while stirring. To the resultantsolution were successively added 467.7 g of telluric acid (H₆ TeO₆) and1,632.0 g of ammonium paramolybdate [(NH₄)₆ Mo₇ O₂₄ ·4H₂ O], to therebyobtain a solution. To the obtained solution was added 3,000 g of silicasol having a SiO₂ content of 30 wt %, followed by addition of aniobium-containing solution (which was prepared by a method in which345.6 g of 25 wt % aqueous ammonia and 1,336.5 g of water were mixed toeach other and 834.7 g of niobium hydrogenoxalate [Nb(HC₂ O₄)₅ ·nH₂ O](Nb₂ O₅ content: 16.2% by weight) was dissolved in the resultantsolution), to thereby obtain a slurry. The obtained slurry was subjectedto spray drying at a temperature of about 200° C. to obtain a driedparticulate catalyst composition precursor. The obtained catalystcomposition precursor was heat-treated by means of an electric kiln inan atmosphere of air at 275° C. for 2 hours, and then subjected tocalcination at 600° C. for 2 hours under a stream of nitrogen gas havingan oxygen concentration of only 1 ppm, to thereby obtain a catalystcomposition.

Example 1

Using the catalyst composition obtained in the Reference Example above,an ammoxidation reaction of propane was conducted as follows.

30 g of the obtained catalyst composition was charged into a Vycor glassfluidized-bed reactor having an inner diameter of 25 mm. Thefluidized-bed reactor containing the catalyst composition was placed inan electric furnace. The temperature of the catalyst composition in thereactor was elevated from room temperature to 300° C. over 2 hours whilesupplying air into the fluidized-bed reactor at a flow rate of 8.65Ncc/sec (Ncc means cc as measured under the normal temperature andpressure conditions, namely at 0° C. under 1 atm.). Then, thetemperature of the catalyst composition was further elevated from 300°C. to 430° C. over 2 hours while supplying a gaseous mixture of air andammonia having an ammonia content of 2% by volume into the reactor at aflow rate of 8.65 Ncc/sec. At a point in time when the temperature ofthe catalyst composition reached 430° C., the concentration of oxygen inthe gaseous mixture effluent from the outlet of the reactor(hereinafter, frequently referred to simply as "oxygen concentration atthe reactor outlet") was about 18% by volume.

Then, the supply of air and ammonia into the fluidized-bed reactor wasstepwise changed to a feeding of gaseous feedstocks of propane, ammoniaand air wherein the [propane: ammonia: air] volume ratio is1.0:1.0:13.0. The stepwise change of the composition of a gaseousmixture in the reactor to a composition suitable for the ammoxidationreaction was performed by changing the gas in the reactor ten times by a1/10 volume of the entire volume at each time at intervals of about 10minutes. Finally, the gaseous feedstocks were fed into the reactor at aflow rate of 8.65 Ncc/sec, to thereby effect an ammoxidation reaction ofpropane to produce acrylonitrile.

During the ammoxidation reaction of propane, the reaction temperaturewas maintained at 430° C., the reaction pressure was maintained at 0.5kg/cm² ·G and the contact time between the catalyst composition and thegaseous feedstocks was maintained at 2.0 sec·g/cc.

The results of the ammoxidation reaction were evaluated in terms of theconversion (%) of propane and the yield (%) of acrylonitrile as definedby the above formulae. As a result, it was found that the conversion ofpropane and the yield of acrylonitrile were 72.2% and 44.0%,respectively.

The results of the above ammoxidation reaction are shown in Table 1.

Comparative Example 1

Substantially the same procedure as in Example 1 was repeated, exceptthat the temperature of the catalyst composition in the fluidized-bedreactor was gradually elevated from room temperature to 430° C. over 4hours while supplying air into the fluidized-bed reactor at a flow rateof 8.65 Ncc/sec. At a point in time when the temperature of the catalystcomposition reached 430° C., the oxygen concentration at the reactoroutlet was about 21% by volume.

The results of the ammoxidation were evaluated in terms of theconversion (%) of propane and the yield (%) of acrylonitrile as definedby the above formulae. As a result, it was found that the conversion ofpropane and the yield of acrylonitrile were 60.0% and 31.2%,respectively.

The results of the above ammoxidation reaction are shown in Table 1.

Example 2

The temperature elevation of the catalyst composition in thefluidized-bed reactor was conducted in substantially the same manner asin Example 1 except that, instead of the gaseous mixture of air andammonia having an ammonia content of 2% by volume in Example 1, agaseous mixture of air and ammonia having an ammonia content 10% byvolume is supplied into the reactor during the temperature elevation ofthe catalyst composition from 300° C. to 430° C. At a point in time whenthe temperature of the catalyst composition reached 430° C., the oxygenconcentration at the reactor outlet was about 11% by volume.

Then, substantially the same procedure for ammoxidation reaction ofpropane as in Example 1 was repeated.

The results of the ammoxidation reaction were evaluated in terms of theconversion (%) of propane and the yield (%) of acrylonitrile as definedby the above formulae. As a result, it was found that the conversion ofpropane and the yield of acrylonitrile were 72.6% and 44.5%,respectively.

The results of the above ammoxidation reaction are shown in Table 1.

Comparative Example 2

The temperature elevation of the catalyst composition in thefluidized-bed reactor was conducted in substantially the same manner asin Example 1 except that, instead of the gaseous mixture of air andammonia having an ammonia content of 2% by volume in Example 1, agaseous mixture of nitrogen and air having an oxygen concentration of11% by volume was supplied into the reactor during the temperatureelevation of the catalyst-composition from 300° C. to 430° C. At a pointin time when the temperature of the catalyst composition reached 430°C., the oxygen concentration at the reactor outlet was about 11% byvolume.

Then, substantially the same procedure for ammoxidation reaction ofpropane as in Example 1 was repeated.

The results of the ammoxidation reaction were evaluated in terms of theconversion (%) of propane and the yield (%) of acrylonitrile as definedby the above formulae. As a result, it was found that the conversion ofpropane and the yield of acrylonitrile were 61.8% and 34.5%,respectively.

The results of the above ammoxidation reaction are shown in Table 1.

Example 3

The temperature elevation of the catalyst composition in thefluidized-bed reactor was conducted in substantially the same manner asin Example 1 except that, instead of the gaseous mixture of air andammonia having an ammonia content of 2% by volume in Example 1, agaseous mixture of air and propane having a propane content of 1% byvolume was supplied into the reactor during the temperature elevation ofthe catalyst composition from 300° C. to 430° C. At a point in time whenthe temperature of the catalyst composition reached 430° C., the oxygenconcentration at the reactor outlet was about 17% by volume.

Then, substantially the same procedure for ammoxidation reaction ofpropane as in Example 1 was repeated.

The results of the ammoxidation reaction were evaluated in terms of theconversion (%) of propane and the yield (%) of acrylonitrile as definedby the above formulae. As a result, it was found that the conversion ofpropane and the yield of acrylonitrile were 70.6% and 41.0%,respectively.

The results of the above ammoxidation reaction are shown in Table 1.

Example 4

The temperature elevation of the catalyst composition in thefluidized-bed reactor was conducted in substantially the same manner asin Example 1 except that, instead of the gaseous mixture of air andammonia having an ammonia content of 2% by volume in Example 1, agaseous mixture of air and propylene having a propylene content of 3.5%by volume was supplied into the reactor during the temperature elevationof the catalyst composition from 300° C. to 430° C. At a point in timewhen the temperature of the catalyst composition reached 430° C., theoxygen concentration at the reactor outlet was about 8% by volume.

Then, substantially the same procedure for ammoxidation reaction ofpropane as in Example 1 was repeated.

The results of the ammoxidation reaction were evaluated in terms of theconversion (%) of propane and the yield (%) of acrylonitrile as definedby the above formulae. As a result, it was found that the conversion ofpropane and the yield of acrylonitrile were 72.8% and 44.2%,respectively.

The results of the above ammoxidation reaction are shown in Table 1.

Example 5

Using the catalyst composition obtained in Reference Example above, anammoxidation reaction of propane was conducted as follows.

1,000 g of the obtained catalyst composition was charged into astainless steel (SUS304) fluidized-bed reactor having an outer diameterof 3 inches. The fluidized-bed reactor containing the catalystcomposition was placed in an electric furnace. The temperature of thecatalyst composition in the reactor was elevated from room temperatureto 300° C. over 2 hours under a pressure of 0.5 kg/cm² ·G whilesupplying air into the fluidized-bed reactor from the bottom thereof ata flow rate of 200 Ncc/sec. Then, the temperature of the catalystcomposition was further elevated from 300° C. to 430° C. over 2 hourswhile supplying ammonia into the reactor through a nozzle located 2 cmabove the bottom of the reactor, wherein the flow rate of the ammoniawas initially 2.78 Ncc/sec and was increased by 2.78 Ncc/sec per about10 minutes while maintaining the total flow rate of the gases suppliedinto the reactor at 200 Ncc/sec. At a point in time when the temperatureof the catalyst composition reached 430° C., the oxygen concentration atthe reactor outlet was about 6% by volume.

Then, the supply of air and ammonia into the fluidized-bed reactor wasstepwise changed to a feeding of gaseous feedstocks of propane, ammoniaand air into the reactor, wherein the propane and ammonia are fedthrough a nozzle located 2 cm above the bottom of the reactor, whereasthe air is fed from the bottom of the reactor, and wherein the [propane:ammonia: air] volume ratio is 1.0:1.05:13.0. The stepwise change of thecomposition of a gaseous mixture in the reactor to a compositionsuitable for the ammoxidation reaction was performed by changing the gasin the reactor ten times by a 1/10 volume of the entire volume at eachtime at intervals of about 20 minutes. Finally, the gaseous feedstockswere fed into the reactor at a flow rate of 200 Ncc/sec, to therebyeffect an ammoxidation reaction of propane to produce acrylonitrile.

The results of the ammoxidation reaction were evaluated in terms of theconversion (%) of propane and the yield (%) of acrylonitrile as definedby the above formulae. As a result, it was found that the conversion ofpropane and the yield of acrylonitrile were 75.6% and 45.0%,respectively.

The results of the above ammoxidation reaction are shown in Table 1.

Comparative Example 3

The temperature elevation of the catalyst composition in thefluidized-bed reactor was conducted in substantially the same manner asin Example 5 except that the temperature of the catalyst composition inthe reactor was elevated from room temperature to 430° C. over 4 hourswhile supplying air into the reactor. At a point in time when thetemperature of the catalyst composition reached 430° C., the oxygenconcentration at the reactor outlet was about 21% by volume.

Then, substantially the same procedure for ammoxidation reaction ofpropane as in Example 5 was repeated.

The results of the ammoxidation reaction were evaluated in terms of theconversion (%) of propane and the yield (%) of acrylonitrile as definedby the above formulae. As a result, it was found that the conversion ofpropane and the yield of acrylonitrile were 65.0% and 32.5%,respectively.

The results of the above ammoxidation reaction are shown in Table 1.

Comparative Example 4

A catalyst composition comprising a silica carrier having supportedthereon an oxide catalyst, wherein the silica carrier is present in anamount of 30% by weight, based on the total weight of the silica carrierand the oxide catalyst and wherein the oxide catalyst comprises acompound oxide described in Working Example 6 of U.S. Pat. No. 5,334,743and represented by the formula: Mn₀.4 V₀.05 Mo₀.4 O₁.75, was prepared asfollows.

546.3 g of ammonium paramolybdate [(NH₄)₆ Mo₇ O₂₄ ·4H₂ O] and 45.7 g ofammonium metavanadate (NH₄ VO₃) were dissolved in 1,100.2 g of water. Tothe resultant solution was added 1,000 g of silica sol having a SiO₂content of 30 wt %, followed by addition of a manganese-containingsolution which was prepared by dissolving 897.1 g of manganese nitrate[Mn(NO₃)₂ ·6H₂ 0] in 410.0 g of 16.6 wt % nitric acid, to thereby obtaina slurry. The obtained-slurry was subjected to spray drying at atemperature of 200° C., to obtain a dried particulate catalystcomposition precursor. The obtained catalyst composition precursor washeat-treated by means of an electric kiln in an atmosphere of air at300° C. for 2 hours, and then subjected to calcination in an atmosphereof air at 500° C. for 4 hours, to thereby obtain a catalyst composition.

Using the catalyst composition obtained above, an ammoxidation reactionof propane was conducted as follows.

Substantially the same temperature elevation operation as in Example 1was repeated except that, instead of the catalyst composition used inExample 1, the catalyst composition obtained above was used, and that,instead of the final elevation temperature (430° C.) used in Example 1,the temperature of the catalyst composition was elevated to 450° C. At apoint in time when the temperature of the catalyst composition reached450° C., the oxygen concentration at the reactor outlet was about 18% byvolume.

Then, an ammoxidation reaction of propane was conducted in substantiallythe same manner as in Example 1 except that the ammoxidation reactiontemperature was 450° C. instead of 430° C., the contact time between thecatalyst composition and the gaseous feedstocks was 1.9 sec·g/cc(instead of 2.0 sec·g/cc) and the [propane: ammonia: air] volume ratiowas 1.0:1.0:11.3 (instead of 1.0:1.0:13.0).

The results of the ammoxidation reaction were evaluated in terms of theconversion (%) of propane and the yield (%) of acrylonitrile as definedby the above formulae. As a result, it was found that the conversion ofpropane and the yield of acrylonitrile were 22.5% and 0.6%,respectively.

The results of the above ammoxidation reaction are shown in Table 1.

Comparative Example 5

Using the catalyst composition obtained in Comparative Example 4, anammoxidation reaction of propane was conducted as follows.

Substantially the same temperature elevation operation as in ComparativeExample 1 was repeated except that, instead of the catalyst compositionused in Comparative Example 1, the catalyst composition obtained inComparative Example 4 was used, and that, instead of the final elevationtemperature (430° C.) used in Comparative Example 1, the temperature ofthe catalyst composition was elevated to 450° C. At a point in time whenthe temperature of the catalyst composition reached 450° C., the oxygenconcentration at the reactor outlet was about 21% by volume.

Then, substantially the same procedure for ammoxidation reaction ofpropane as in Comparative Example 4 was repeated.

The results of the ammoxidation reaction were evaluated in terms of theconversion (%) of propane and the yield (%) of acrylonitrile as definedby the above formulae. As a result, it was found that the conversion ofpropane and the yield of acrylonitrile were 22.3% and 0.6%,respectively.

The results of the above ammoxidation reaction are shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Examples                                                                            Type of the gas(es)                                                                          Oxygen concen-             Yield of                        and supplied into the reactor tration at the  Conversion acrylo-                                                             Comparative during the                                                       temperature reactor                                                           outlet [Propane/ammonia/                                                      of propane nitrile                                                             Examples elevation from                                                      300°0 C. to                                                            430° C. at                                                             430° C. (% by                                                          volume) air] volume ratio                                                     (%) (%)                       __________________________________________________________________________    Example 1                                                                           air + ammonia (ammonia                                                                       about 18    1.0/1.0/13.0                                                                           72.2  44.0                             content: 2% by volume)                                                       Example 2 air + ammonia (ammonia about 11 1.0/1.0/13.0 72.6 44.5                                                              content:- 10% by                                                            volume)                         Example 3 air + propane (propane about 17 1.0/1.0/13.0 70.6 41.0                                                              content: 1% by volume)                                                       Example 4 air + propylene                                                     (propylene about 8                                                           1.0/1.0/13.0 72.8 44.2                                                          content: 3.5% by                                                            volume)                         Example 5 air + ammonia.sup.1) about 6 1.0/1.05/13.0 75.6 45.0                Comparative air about 21 1.0/1.0/13.0 60.0 31.2                               Example 1                                                                     Comparative air + nitrogen about 11 1.0/1.0/13.0 61.8 34.5                    Example 2 (oxygen concentration:                                               11% by volume)                                                               Comparative air about 21 1.0/1.05/13.0 65.0 32.5                              Example 3                                                                     Comparative air + ammonia.sup.2) (ammonia about 18.sup.3) 1.0/1.0/11.3                                                      22.5 0.6                        Example 4 content: 2% by volume)                                              Comparative air.sup.2) about 21.sup.3) 1.0/1.0/11.3 22.3 0.6                  Example 5                                                                   __________________________________________________________________________     Note .sup.1) While maintaining the total flow rate of the gases supplied      into the reactor at 200 Ncc/sec, the flow rate of ammonia was increased b     2.78 Ncc/sec per about 10 minutes.                                            Note .sup.2) Supplied into the reactor during the temperature elevation       from 300° C. to 450° C.                                         Note .sup.3) Measured at a temperature of 450° C.                 

INDUSTRIAL APPLICABILITY

In a process for producing acrylonitrile or methacrylonitrile byammoxidation in the presence of.a catalyst composition, by virtue of theunique operation for temperature elevation of the catalyst bed usingboth a molecular oxygen-containing gas and a combustible gas when thetemperature of the catalyst composition is 300° C. or higher, theprocess of the present invention is advantageous in that the temperatureelevation of a catalyst comprising a compound oxide of molybdenum,vanadium, niobium and at least one element selected from tellurium andantimony can be performed without suffering a deterioration of thecatalytic activity of the catalyst during the temperature elevation ofthe catalyst, thereby allowing the catalyst to fully exhibit excellentperformance thereof.

What is claimed is:
 1. A process for producing acrylonitrile ormethacrylonitrile from propane or isobutane by ammoxidation at atemperature in the range of from 380 to 500° C. (ammoxidation reactiontemperature) in a fluidized-bed reactor containing a catalystcomposition comprising a carrier having supported thereon an oxidecatalyst, said oxide catalyst comprising a compound oxide of molybdenum,vanadium, niobium and at least one element selected from the groupconsisting of tellurium and antimony,said process comprising:(1)providing a fluidized-bed reactor containing said catalyst compositionpreheated to a temperature of not lower than 300° C. and lower than saidammoxidation reaction temperature; (2) elevating the temperature of saidpreheated catalyst composition in said fluidized-bed reactor, whilesupplying into said fluidized-bed reactor a molecular oxygen-containinggas together with a combustible gas capable of combustion by reactionwith said molecular oxygen in the presence of said catalyst composition,until the temperature of the catalyst composition reaches saidammoxidation reaction temperature; and (3) changing the supply of thecombustible gas and the molecular oxygen-containing gas into saidfluidized-bed reactor to a feeding of propane or isobutane, ammonia andmolecular oxygen into said fluidized-bed reactor when the temperature ofthe catalyst composition reaches said ammoxidation reaction temperature,to thereby effect an ammoxidation reaction of said propane or isobutane,thus producing acrylonitrile or methacrylonitrile.
 2. The processaccording to claim 1, wherein said combustible gas is at least onecompound selected from the group consisting of C₁ -C₈ alkanes, C₂ -C₈alkenes, C₂ -C₄ alkynes, C₄ -C₅ dienes, C₃ -C₈ cycloalkanes, C₄ -C₈cycloalkenes, C₆ -C₉ aromatic hydrocarbons, C₁ -C₈ alcohols, C₂ -C₇ethers, C₁ -C₃ aldehydes, C₂ -C₃ epoxides, C₂ -C₈ ketones, C₁ -C₄nitrites, C₁ -C₄ carboxylic acids, C₂ -C₅ esters, C₁ -C₆nitrogen-containing organic compounds, C₁ -C₄ sulfur-containing organiccompounds, hydrogen, ammonia, carbon monoxide, hydrogen sulfide andcarbon disulfide.
 3. The process according to claim 1, wherein saidcombustible gas is at least one compound selected from the groupconsisting of propane, isobutane, propylene, isobutene, methanol,ethanol, propanol, hydrogen, ammonia and carbon monoxide.
 4. The processaccording to claim 1, wherein said combustible gas is ammonia.